--
Apart from being able to deduce it from Section 4.3, it is not absolutely clear
from Section 4 that the colon has special meaning. That is that all prefixes
now and in the future are delimited by the colon.
(This is important because, absent a colon, there is no way to distinguish an
non-colon user prefix from any registered prefix.) This means that:
- Future definitions of tag values might not realise that they are
supposed to use a colon - you should clarify that all prefixes end
with a colon noting that the colon is not a separator but is part of
the prefix. This does beg the question about separators in the
prefixes and in the tag values
- Prefixes that contain colons will cause confusion and so you should
probably make it a 'MUST NOT'
- Tag values (after the prefix) that contain colons may cause
confusion so you should probably make this a RECOMMENDation,
although 4.2 suggests the use of colons as further separators.
An alternative to all this is that you define the colon as the separator, and
change the tag names to not include colons.
But 9.1 makes it pretty clear that you expect all registered prefixes to end
with a colon.
[Qin Wu] That's really a good comment, so Tag = Tag prefix+ Tag Value, Colon is
part of Tag prefix if you expect all registered prefix to end with a colon.
The question is whether we see colon as separator or portion of the tag prefix.
Do we need to make tag prefix is mandatory to have for a tag?
[AF] I don't really mind.
The closest to what you have is...
- Tag prefix is not mandatory
- All tag prefixes MUST end with a colon
- Colons MUST NOT be used within a prefix
- Colons SHOULD NOT be used in a tag value If you want to, you could specify a
character to be used as a separator within prefixes and values (such as a
period).
[Qin Wu-1] That's a good summary. I will incorporate some of these principles
into the updated draft. In addition, I think Colons can be used within a tag
value, "entno:vendor-defined-classifier" is one of examples used for vendor tag.
[AF2] Sounds good.
The colon in a tag value is allowed by "SHOULD NOT", but I wanted to avoid the
confusion between a tag value that does not use a prefix but contains a colon,
and a tag that has a prefix and a value.
For example, ietf:foo should be a tag comprising the prefix ietf: and the value
foo. But a non-prefixed tag could legitimately be ietf:foo.
That example is a bit silly, but consider that someone makes a non-prefix tag
iab:bah and deploys the code. Tomorrow the IETF decides that there should be a
registered prefix iab: Now we have collisions.
[QW2]Your clarification makes sense, I think what we should first avoid is 3
prefix we defined in this draft appear in the tag value, in addition, one rule
we have already added is
" this document is purposefully not specifying any structure on (i.e.,
restricting) the tag values.", do we need to add further restriction to limit
"iab:" to be part of tag value.
Another choice is to we set rule that it is mandatory to have prefix for each
data node tag. Is this too restrictive?
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